Qmail SMTP Integration Guide
Guide to integrate Mailazy with your Qmail application
You need to complete these given prerequisites, you can skip the step if you have already completed.
Qmail does not come with SMTP authentication functionality installed. However you can add the netqmail TLS+SMTPauth patch.
Alternately, you can take a look at Fehcom's very complete description of authentication on mail servers, or just jump down to the section about configuring SMTPAUTH for qmail.
In general, you will need to add the following to /var/qmail/control/smtproutes, but you should verify the actual path and file you need to update.
:smtp.mailazy.com:587 mailazy_apikey mailazy_secret
As with all configuration changes, make sure to restart qmail.